The outgoing US Secretary of State Rex Tillerson has told his employees to 'never lose sight of personal integrity'.

Mr Tillerson was giving farewell remarks before he steps down from the role.

He was fired earlier this month after just over a year in the job.

The former Exxon chief is being replaced by the current director of the CIA, Mike Pompeo.

In a tweet at the time, US President Donald Trump said: "Mike Pompeo, Director of the CIA, will become our new Secretary of State. He will do a fantastic job! Thank you to Rex Tillerson for his service!".

The pair are widely reported to have clashed on a wide-range of issues over the past year, with US media having repeatedly suggested Mr Tillerson's time in the role was limited.

Mr Tillerson - who had no previous government experience - was one of Donald Trump's most notable and surprising major cabinet appointments.

File photo show US President Donald Trump (left) with Rex Tillerson | Image: Rey Baniquet/Zuma Press/PA Images

Speaking after firing Mr Tillerson, Mr Trump claimed: "Rex and I have been talking about this for a long time.

"We got actually along quite well, but we disagreed on things.

"When you look at the Iran deal - I think it's terrible, I guess he thought it was OK".

The 65-year-old did not speak to Mr Trump before he was sacked and has not been given a reason for his dismissal, a top aide has said.

In remarks to staff on Thursday, Mr Tillerson said: "The country faces many challenges - in some instances perplexing foreign affairs relationships, and in other instances serious national security threats.

"In these times, your continued diligence and devotion to the State Department's mission has never been more necessary."

"Never lose sight of your most valuable asset, the most valuable asset you possess: your personal integrity.

"Not one of you was gifted it; you were born with it. It belongs to you, and always has and will belong to you and you alone.

"Only you can relinquish it or allow it to be compromised."

"In closing, I'd like to ask that each of you undertake to ensure one act of kindness each day towards another person. This can be a very mean-spirited town.

"But you don't have to choose to participate in that.

"Each of us get to choose the person we want to be, and the way we want to be treated, and the way we will treat others."